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jeudi 25 juillet 2013

Understand These Three Estimating Concepts

A lire sur: Method123

Estimate in Phases

One of the most difficult aspects of
planning
projects is the estimating process. It can be hard to know exactly what work will be
needed in the distant future. It can be difficult to define and estimate
work that will be done three months from now. It's harder to estimate
six months in the future. Nine months is even harder. There is
more and more estimating uncertainty associated with work that is
farther and farther out in the future.

A good
approach for larger projects is to
break the work into a series of smaller projects, each of which can be
planned, estimated and managed separately with a much higher likelihood
of success. From an estimating perspective, the closest
project can be estimated more precisely, with the subsequent projects
estimated with a higher level of uncertainty. When one project
completes, the next project can be estimated with a higher degree of
confidence, with estimates refined for the remaining projects. This
technique also provides checkpoints at the end of each project so that
the entire initiative can be revalidated based on current estimates to
ensure that it is still viable and worth continuing.

Estimate Fixed Costs and Variable
Costs

You may hear the terms fixed and variable
cost when you are estimating the cost of a project. Variable costs are
those that change relative to how many units are being used. An obvious
variable cost on a project is contract labor. The more hours you use
from a contactor, the more the cost to the project. The
cost of contract labor is variable depending on the number of hours
worked.

Fixed costs are those that are basically
the same for the project regardless of the resources being used. For
instance, if you were building a house, the cost of
the lot would be fixed and would not change based on
the size of the house you built. Similarly, if you outsource part of a project to a
third party for a fixed price, it becomes a fixed cost to the project as
well. Even if the work takes longer or shorter than estimated, your
project cost should still be the agreed upon fixed cost.

Estimate Time-Constrained and
Resource-Constrained Activities

Activities can be classified as time or
resource-constrained based on whether the duration can change if more
resources are applied. An activity is resource-constrained if the
duration changes based on the number of resources applied. For instance,
you might estimate that it will take 80 hours for one person to build a
roof on top of a house. If the person worked forty hours per week, it
would take two weeks to complete the job. If you applied two people to
the job, the effort is still be 200 total effort hours, but the job
would only take one week to complete.

On the other hand, if an activity is
time-constrained, the duration remains the same regardless of the number
of resources applied. For example, lets say one person attends a three-day class. If you send two people to the
class, the class does not get shorter; it still takes three days.
Likewise, the time it takes for concrete to dry, or to mail a letter, is
not impacted by the number of people involved. They just take a certain
amount of time. If you find that applying resources has no impact on the
project duration (or very little impact), then the activity is
time-constrained.